The Sony a7S III has been the undisputed king of high ISO performance since 2020. It shares its sensor with the FX3 and FX6, and for years, no camera has come close to touching it in low light. But the new Panasonic S1II is here with a partially stacked sensor (the same one found in the Nikon Z6III), and Panasonic has a long history of squeezing every last drop of performance out of whatever sensor they get their hands on.
So I put both cameras head to head in a controlled low light test to see how the S1II stacks up. Here’s what I found.
The Test Setup
Both cameras start at the same base ISO of 640, which is a nice even playing field. The Sony a7S III is recording in XAVC HS 4K, which is H.265 and arguably the best quality codec the camera offers. A quick tip here: some people assume the XAVC S-I codec is higher quality because it produces larger file sizes, but in all of my low light testing over the years, the XAVC HS codec actually has slightly better noise reduction and produces a cleaner image at high ISOs. If you’re shooting the a7S III in low light, you want XAVC HS.
For the S1II, I’m shooting in MOV format with H.265 at 5.9K resolution. I know that’s a higher resolution than the 4K the a7S III is shooting in, but I didn’t want to introduce any potential image quality issues from downscaling in-camera, which can sometimes soften the image. So we’re comparing native resolution from both cameras, both in H.265, both in their respective log profiles (S-Log3 on the Sony, V-Log on the Panasonic), and no color grading applied so you can see the raw noise as clearly as possible.
The Lower ISO Range: Clean All the Way Up
Cranking through the early ISO values, both cameras look excellent. ISO 800, 1250, 1600, 2000, 2500 all look fantastic. At ISO 3200 the S1II is handling it with ease, which is impressive when you remember that on an older camera like the Panasonic GH5, ISO 3200 was basically the limit before things got too noisy. The full-frame sensor and newer technology make a huge difference here.
At ISO 4000, things get interesting on the S1II. This is the ISO right below its second base ISO of 5000, and that positioning shows. There’s some noticeable noise creeping in. It’s not unusable, but it’s definitely the weakest link in the S1II’s ISO range.
Dual Base ISO: Why It’s Such a Big Deal
At ISO 5000 on the S1II, something really cool happens. The image gets significantly cleaner. That’s because ISO 5000 is the second base ISO of the S1II, meaning anything filmed at ISO 5000 is going to look just as clean as if you filmed it at ISO 640. The camera essentially resets its noise floor at that point.
The a7S III has the same dual base ISO feature, but its second base ISO is much higher at 12,800. This is one of the most interesting differences between these two cameras, and it’s worth thinking carefully about which one is more useful for how you actually shoot.
The S1II’s ISO 5000 second base ISO is arguably more practical for general filmmaking situations. If you’re shooting in a dark environment where you need to push to ISO 5000, you can do it cleanly. The a7S III’s second base ISO of 12,800 is extraordinarily powerful, but there’s also such a big jump between 640 and 12,800 that it can sometimes be tricky to manage exposure between those two points. At ISO 12,800, you often need an ND filter to avoid overexposure, even in a moderately lit room.
ISO 10,000: A Weak Spot on the a7S III
Here’s a tip that I love to share for a7S III owners: ISO 10,000 is one of the noisiest ISOs on the a7S III. Just like ISO 4000 is the weakest on the S1II, ISO 10,000 sits right below the a7S III’s second base ISO of 12,800, and you can see the noise peak there. I’d also avoid ISO 8000 if you can help it. These are the spots where the Sony sensor looks its worst, and they’re easy to avoid once you know about them.
If you want a deeper dive into tips like this, check out my Sony a7S III review for wedding filmmakers and my full a7S III menu setup guide.
The Extreme ISOs: Sony Pulls Away
Once you get above ISO 12,800, both cameras are doing something genuinely impressive. At ISO 16,000, 20,000, and 25,600, both cameras are producing footage that I would call completely usable. Yes, there’s noise, but it’s controlled and workable. It’s wild to say that out loud when I remember shooting with DSLRs years ago where ISO 3200 felt like a gamble.
At ISO 32,000 and 40,000, the Sony starts to pull ahead more noticeably. The S1II continues to hold on, but you can see more degradation in the shadows compared to the a7S III, which stays remarkably clean.
ISO 51,200 is the maximum for the S1II, and at that ceiling, I honestly think you could still use the footage if you were in a genuinely dark environment and needed it. For a camera that isn’t specifically marketed as a low-light powerhouse, that’s a legitimately impressive result.
Where the a7S III Goes Into Another Dimension
The S1II taps out at 51,200. The Sony a7S III is just getting warmed up.
ISO 64,000, 80,000, and then 102,400, which is the standard maximum of the a7S III (anything above this is technically “extended”), and it still looks usable. I’ve been asked many times over the years what the maximum usable ISO is on the a7S III and FX3, and my honest answer is basically all of them. Other cameras force you to draw a line in the sand. The Sony sensor rarely does.
Pushing into the extended ISOs, things get progressively muddier. At ISO 128,000, you can see detail starting to soften and the image becoming overexposed even in a very dark room. At 204,800 and 256,000, sharpness continues to break down. And at the absolute maximum of ISO 409,600, the image is overexposed, swampy, and the noise is dancing everywhere. But here’s the thing: when you set that ISO 409,600 image from the Sony next to the S1II sitting at its max of ISO 51,200, the Sony is still dramatically brighter. It’s a remarkable engineering achievement.
The Sony sensor inside the a7S III, FX3, and FX6 is still the king. But the margin is smaller than it used to be.
So Which Camera Should You Choose?
This really comes down to how and where you film.
If you film in moderately dark conditions and want a second base ISO that’s practical and easy to manage in real-world situations, the S1II’s ISO 5000 second base is genuinely useful and less tricky to expose around than the Sony’s 12,800.
If you are a wedding filmmaker who regularly finds yourself in dark reception halls with limited lighting control, or you commonly film in extremely dark environments like night shoots outdoors, the a7S III and FX3 still come out on top. You’re going to lean on those upper ISOs more often, and the Sony handles them better. That said, the margin of victory is slimmer than it’s ever been. The S1II looking this good at ISO 25,600, 32,000, and 51,200 would have been jaw-dropping even a couple of years ago.
For more info on how the S1II performs as a full wedding and documentary camera, check out my Panasonic S1II menu setup guide. And if you’re looking to get your editing and color workflow locked in for either of these cameras, check out my color presets and LUTs that work across Sony, Panasonic, Nikon, and iPhone. Want to level up your overall filmmaking and editing skills? My Edit Videos Like a Pro guide is a great place to start.